Arc gas expansion chamber for high voltage termination bushings



May 19, 1970 w. A. MCMORRIS ARC GAS EXPANSION CHAMBER FOR HIGH VOLTAGETERMINATION BUSHINGS Filed Jan. 8, 1968 2 Sheets-Sheet 1 A w y 9W 5 3 kUnited States Patent US. Cl. 339-111 3 Claims ABSTRACT OF THE DISCLOSUREThe application discloses an electrical termination bushing forhermetically sealed high voltage devices such transformers having aninternal sealed chamber or external sealed metallic pressure chamberattached thereto for receiving and cooling arc gases generated duringload making or load breaking and for limiting gas pressures to amagnitude which will not damage the bushing. One embodiment comprises anannular metallic chamber threaded to an inner end extension of a bushingcontact structure and a bushing well formed around the chamber, contact,and an included bushing insert carrying the contact, or a sealed chamberformed in a bushing. A second embodiment contemplates the attachment ofa sealed metallic cup to the inner end of a modified conventionalbushing by a hollow stud directly connected to the contact structure ofthe bushing and projecting through the inner end of the bushing casinginto the transformer.

BACKGROUND OF THE INVENTION This invention relates to terminationbushings and, more particularly to improvements in high voltagetermination bushings adapted for use in hermetically sealed devices suchas transformers.

As is well known to those skilled in the high voltage termination art,the electrical arcing caused by load-make and load-break operations is along standing problem which has been approached in several ways. One ofthe most common solutions utilized in existing high voltage terminationscomprises the placement of a gas generating solid material in followerrelationship with the contacts so that, when an arc is created, it willreact with the solid material to liberate arc extenguishing gases. Thisscheme has worked well to limit the arcing; but, the proper treatmentand handling of the generated gases has now presented a new problem inthat the resulting extreme pressures are capable of severely damagingthe bushing or ejecting the terminator contact which may ultimatelyresult in personal injury, power failures and expensive maintenance.Even in the absence of a supplied arc extinguishing gas, an ambient gassubjected to high arc current under fault conditions can cause bushingrupture.

In meeting this pressure problem, many existing terminations aredesigned with a tubular core in which contact is made and through whichthe arc gases are ducted. When utilized in connection with ahermetically sealed device such as a transformer, the core is extendedthrough the inner end of the bushing and fitted with a one way valve tovent the gases into the transformer. This method is consideredundesirable in that the vented gases violate the hermetical seal andcontaminate the dielectric liquid placed within the transformer.

As is well understood, these transformers and like electrical apparatusare sealed to prevent the entry of oxygen or moisture which would beharmful to the operation of the electrical apparatus. The pressurewithin this type of apparatus normally varies up and down as itstemeprature changes with varying load, so that at any particular time itmay be above or below the outside pressure. Under these icecircumstances there is a possibility that the valve could admit gas intothe sealed apparatus when its internal pressure was low. Not only wouldthe oxygen and moisture in such admitted gas be harmful to theelectrical apparatus, but it would also shift the range of the internalpressure excursions, which could result in peak pressure exceeding thatfor which the apparatus was designed. Further, the gases which aredischarged into the electrical apparatus during arcing of the contactscarry soot and droplets of molten metal and other contaminants into theelectrical apparatus which are detrimental to its operation.

Accordingly, it is one object of this invention to provide an improvedhigh voltage termination bushing for use in transformers or the likewhich bushing will withstand the pressures generated by are gases whilesimultaneously maintaining the hermetical seal of the transformer.

A further object of this invention is to provide an inexpensive pressureexpansion chamber adapted for use with existing conventional highvotlage termination bushings to limit are gas pressures to acceptablemagnitudes while preserving the hermetical seal of an electrical devicewithin which the bushing is mounted.

SUMMARY OF THE INVENTION In carrying out this invention, an improvedhigh voltage termination bushing is provided, having an elongated casingwith a hollow core. A first electrical contact is positioned within thecore and means for receiving and holding a second electrical contact areformed at one end of the casing. A sealed chamber is provided having aconnection with the first contact and positioned adjacent the other endof the casing in gas pressure communication with the electricalconnection area. Means are provided for hermetically sealing the overallbushing casing to an electrical device.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims which particularly point out and distinctly claim the inventionwhich is sought to be protected, the preferred embodiments are disclosedin the following descriptions in connection with the accompanyingdrawings in which:

FIG. 1 is an exploded sectional elevation view of an improved highvoltage bushing showing an internal gas pressure expansion chamberaccording to one form of this invention, together with a conventionalbayonet type terminator;

FIG. 2 is an enlarged sectional view of one form of an internallyinstalled pressure chamber taken along its axis according to theembodiment of the invention shown in FIG. 1;

FIG. 3 is a partial sectional elevation view of an improved high voltagebushing according to this invention showing another form of internalpressure chamber;

FIG. 4 is a sectional elevation view of one type of existing bushingwhich shows the external attachment of a gas pressure expansion chamberaccording to another form of this invention; and

FIG. 5 is an enlarged sectional elevation view of the externally mountedchamber taken along its axis.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, inwhich like numerals are used to indicate like parts throughout thevarious views thereof, this invention in one embodiment, is shown inFIG. 1 as an improved high voltage bushing 10 with an internallyinstalled gas pressure expansion chamber 12. The bushing 10 is of thekind used in hermetically sealed electrical apparatus, such as atransformer, and includes a composite, substantially cylindricalhousing, comprising an outer bushing well 14 and an inner bushing insert16.

The bushing well 14 may be molded to a metal plate or wall member forhermetically sealing to a transformer in the manner more fully describedand claimed in application Ser. No. 470,068, filed July 7, 1965 forPlastic Bushing for Electrical Apparatus and Method of Making, in thenames of F. S. Nichols, G. F. Lipsey and G. C. Nonken, and assigned tothe same assignee as this invention, now Pat. No. 3,388,212.

The bushing well 14 is constructed of an insulating material, such as amolded epoxy resin and is formed with a large hollow core. The coreextends from the top of the housing well 14 to a wall 18 formed at thebottom in which is formed an aperture 20 which is concentric with thecore but of lesser diameter.

The cylindrical gas pressure expansion chamber 12 is inserted into thelower end of the hollow core of the bushing well 14. The chamber 12 ispreferably constructed of a good heat conducting metal such as copper.As is best shown in FIG. 2, chamber 12 is provided with a threaded hole22 in the upper horizontal wall 24 and a threaded bore hole 26 in thebottom horizontal wall 28 which bore hole 26 is of the same size and inline with the threaded hole 22 of the upper wall 24. The bottom wall 28is formed with a downward projecting cylindrical protrusion 30 whichfits through the aperture 20 formed in the bushing well wall 18 and issealed thereto so as to provide a hermetical seal about the bottom ofthe bushing. A contact 32 for connecting internal transformer leads isformed on the outer bottom surface of the protrusion 30.

A tubular metal female contact 34 which is threaded at the lower end 36passes through the hollow core of the bushing well 14 and threadedlyengages chamber 12 at threaded hole 22 and bore hole 26. Gas ports 38are provided in the threaded wall portion 36 of contact 34 to provide ameans for pressure communication between the interior of contact 34 andthe chamber 12. With the contact 34 properly positioned within chamber12, the chamber 12 constitutes an annular gas expansion chamber whichcompletely surrounds the threaded portion of the contact 34.

A sleeve 40 of gas generating material of the same inside and outsidediameters as the contact 34 fits within the core of the bushing insert16 in a position above and in line with tubular contact 34. Whenproperly positioned, the lower end of the bushing insert 1 6 is flushagainst the upper horizontal wall 24 of the chamber 12. The upper lip 42of bushing insert 16 is specially formed as the male member of a bayonetconnection which male member plugs into a female member 44 carriedwithin a terminator housing 46. A male contact 48 is mounted within theterminator housing 46 which contact 48 is designed to engage contact 34in proper electrical connection and which housing 46 is adapted toreceive the upper end of bushing insert 16 and hold it by the bayonetlock created in the aforementioned manner. Contact 48 is provided with afollower 50 of gas generating insulating material similar to sleeve 40.

The bushing well 14 may be mounted and hermetically sealed to atransformer or other electrical apparatus by means of a metal plate 52which is molded within the bushing well 14 and Welded to the transformerwall 54, as described in the aforementioned patent application Ser. No.470,068.

In operation, Whenever a load make or load break is executed and an arcis created, the arc acts upon the gas generating material 40 and 50 toproduce high pressure gases which in turn act to extinguish the arc. Thegases so generated are then vented down through the core of the tubularcontact 34, out through the gas ports 38 and into the chamber 12 asindicated by the arrows in FIG. 1. Within the metal chamber 12, thegases expand and cool so as to dissipate the shock energy caused by thesuddenly generated gases which dissipation ultimately prevents powerfailure and personal or equipment injury.

FIG. 3 shows another form of the invention in which a pressure chamber12a is formed directly in the bushing 10a. As is shown, the bushing 10a,which is preferably molded of an epoxy resin material, has a gasexpansion chamber formed in bushing 10a during molding. A terminalmember 30a, preferably of copper, may also be molded into the bushing10a. Contact member 34a is generally similar to contact 34 of FIG. 1 andis threaded into bore 26a of terminal 30a. Contact 34a is also providedwith ports 38a to permit the generated gases to expand into pressurechamber 12a.

In FIG. 3, bushing 10a is shown as a one piece bushing, rather than thetwo part member shown in FIG. 1. Of course, it will be understood thatthe upper portion of bushing 10a will be similar to bushing 10, so thatit may be connected to any desired type of termination member, forexample that shown in FIG. 1. As shown, a metal plate 52a may be moldedto the bushing 10a, as described in aforementioned patent application470,068. Plate 52:: may then be welded to the wall or cover 54a of anelectrical apparatus. As in the form of invention shown in FIG. 1, thepressure chamber 12a is attached to one end of the electrical contact34a so as to allow expansion of any gases generated during making orbreaking an electrical connection to contact 34a.

FIG. 4 shows a second embodiment of the invention comprising a modifiedconventional terminator bushing 10b comprising an outer bushing well 14band an inner bushing insert 16b. Bushing 1% includes a tubular contact56 which is provided at its lower end with internal threading 58. Ahollow stud 60 which has outside threading at each end 62 and 64 ismated to the internal threading 58 of contact 56 at one end of the stud60 and positioned within the bushing in such a manner that the other endof stud 60 protrudes out through the bottom of bushing well 14b. Acylindrical metallic gas pressure chamber 12b is provided which isformed with a threaded hole 22b in one of the parallel walls on the axisof the cylinder. The threaded hole 22b mates with the protrudingthreaded portion 64 of stud 60 and, when the chamber 12b is properlyconnected to the stud 60, it forms a hermetical seal therewith. Aterminal 66 is provided at the lower end of chamber 12b for electricalconnection to the internal leads of the electrical apparatus.

In operation, when an arc is created during load-make or load-breakactivities, the generated gas supplied by the gas generating material4019 reacting with the arc is vented down through the tubular contact 56and hollow stud 60 into the sealed pressure chamber 12b. The pressurechamber 12b provides sufficient space to contain the suddenly generatedgas and to limit the resulting pressure to a value that will not damagethe bushing or eject the terminator. Likewise, the hermetical seal ismaintained and the dielectric liquids are not contaminated by thegaseous products. The chamber 12b comprising a metal of high thermalconductivity such as copper, cools the gases and is especially effectivein dissipating shock at elevated operating temperatures which may rangeup to C. It will also be seen that this embodiment of the presentinvention is adapted for economical installation in existing terminatorbushings and requires a minimum of modification to the bushing.

From the above description of the preferred embodiments of thisinvention it is believed clear that all of the objects and advantagesherein before set forth have been attained. However, it should beunderstood that while there has been shown and described particularembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom the spirit and scope of the invention.

What is claimed as new and which it is desired to secure by LettersPatent of the United States is:

1. An eiectrical termination bushing having an elongated casing with ahollow core, a first electrical contact within the core, means forreceiving a second electrical contact at one end of the casing to engagein electrical connection with said first electrical contact, means forhermetically sealing said casing to an electrical apparatus housing,said first electrical contact being an elongated tube, one end of saidtube making said electrical connection with the second electricalcontact, threading on the other end of said tube, a gas chambercomprising an annular sealed metallic pressure chamber, a terminal onone end of said gas chamber, the other end of said gas chamber and saidthreaded end of said tube interconnected to provide gas pressurecommunication from said electrical connection end of said tube to saidgas chamber.

2. An electrical termination bushing as set forth in claim 1 in whichsaid gas chamber is threadedly mounted on said threaded end of saidelongated tube and is fitted within the core of said casing.

3. An electrical termination bushing as set forth in claim 1 in whichone end of a hollow stud is threaded to said threaded end of said tubeand said gas chamber is threaded to the other end of said hollow stud,said gas chamber mounted outside the' core of said casing.

References Cited UNITED STATES PATENTS RICHARD E. MOORE, PrimaryExaminer US. Cl. X.R.

